The present invention relates to apparatus for preheating substrates prior to inserting them into a processing chamber for conducting a semiconductor manufacturing process step.
Semiconductor processing chambers are used to provide process environments for the fabrication of integrated circuits and other semiconductor devices on wafers. Wafers are sequentially processed through a series of many different processing steps which include depositions of various layers (metal, insulator and dielectric) on the wafer, each of which may be followed by masking and etching process steps with or without planarization steps also being involved. By selective repetition of the deposition and processing of these layers, integrated circuits may be fabricated on the wafer or substrate.
Deposition and etching processes may be accomplished by various techniques, including various chemical vapor deposition (CVD) processes, physical vapor deposition (PVD) processes, such as sputtering, and plasma processes, to name a few. Most processing chambers used in conducting these processes include a vacuum chamber containing a wafer support member upon which the wafer is placed to be processed. A gas inlet having a mass flow controller, and a throttled exhaust coupled to a vacuum pump through a gate valve communicate with the vacuum chamber to provide the process gas flow and the vacuum conditions required for processing the wafer. A slit valve is provided in the vacuum chamber which allows access by a robot blade used to load the wafer on the wafer support for processing, as well as to remove the wafer from the wafer support and chamber after the process step has been completed.
Many such processes require elevated temperatures for best results. Although it is possible that the wafer support may start out at room temperature initially for processing of a first wafer, this is certainly not the usual case, since there is very little cooling of the wafer support, and certainly not cooling to room temperature during the time that a first wafer is removed and another wafer is loaded to be processed. When a wafer at room temperature is loaded onto a wafer support that is at operating temperature, a phenomenon has been observed where the wafer tends to xe2x80x9cchatterxe2x80x9d or xe2x80x9cdancexe2x80x9d on the wafer support initially after placement there. This phenomenon is believed to be caused when the pins, which support the wafer to allow the robot arm to slide out from between the wafer and wafer support, withdraw to allow the wafer to contact the wafer support. It is believed that cold (i.e., relative to the operating temperature) air is trapped between the wafer and wafer support, and as that air is heated it expands and causes the wafer to chatter as it escapes from between the wafer support and the wafer. This phenomenon, although observed with 200 mm wafer processing, was not as severe a problem as it has become with 300 mm wafer processing, where the chattering is much more pronounced, due to the larger surface area of the wafer, and this is likely to cause misalignment of and/or damage to the wafer.
One way of eliminating the chattering is to leave the wafer on the lift pins for a significant period of time (e.g., about 45 seconds) after placing it in the processing chamber to allow it to heat up prior to contacting it with the chuck. However, this additional time requirement seriously impacts the throughput of the processing. The chattering phenomenon can also be eliminated by preheating the wafers to a temperature significantly above room temperature, although they do not need to be heated all the way up to operating temperature. Such preheating also increases throughput in the processing chamber, since it then takes less time to get the wafer up to processing temperatures. A conventional heater may be used to preheat a wafer substrate. Conventional heaters are generally thick plates, having a thickness of at least 0.5xe2x80x3 up to about 1xe2x80x3, and are often made of cast aluminum or aluminum alloy and having a tube heater filament or embedded metal electrode running through the plate to heat the overall plate. A general idea of such construction can be gained from a reading of the description of the susceptor plate described in U.S. Pat. No. 5,633,073. Although the susceptor plate in the patent is described for use within a processing chamber, a similar construction can be used for preheating.
Conventional heaters have certain drawbacks including the fact that they are relatively thick and bulky, which limits their effectiveness if they are to be used in a stack arrangement for heating of multiple wafers simultaneously. This thickness also translates to a relatively large mass to be heated, and therefor the response time for initial heating up of the heater or changing the steady state temperature of a heater is relatively large (i.e., slow response time). Still further, conventional heaters are relatively heavy and expensive, costing on the order of $4,000 to $5,000 per heater plate.
In view of the foregoing, there remains a need for a heater system that has better response time, is more adaptable to stacked usage, and is less expensive.
A heating chamber assembly is provided with a stack of at least two thick film heater plates forming at least one slot configured to receive a wafer therein. A chamber surrounds the stack and has a door therethrough which opens to allow insertion of wafers and withdrawal of wafers from the assembly. Each slot is alignable with the door for receiving a wafer, or allowing a robot arm to access a wafer already in the slot and withdraw it.
Multiple slots can be provided by stacking enough thick film heater plates to form the desired number of slots. A slot is formed between two thick film heater plates, so that for xe2x80x9cnxe2x80x9d slots, xe2x80x9cn+1xe2x80x9d heater plates are required.
A drive shaft may be mounted to the stack, and the drive shaft extends through the chamber and engages a driver or motor which drives the drive shaft and stack for the purpose of aligning each of the slots with said door as desired. When the door is closed, it forms a pressure seal with the chamber. A sealing mechanism forms a pressure seal around the drive shaft and with the chamber, such that the chamber is capable of maintaining positive pressure. A gas inlet may be provided in the chamber, to enable the passing of a purge gas into the chamber to positively pressurize said chamber.
Each of the thick film heater plates comprises a pair of electrodes through which power is inputted to a resistive circuit to generate heat. A pair of supports underlies and supports each thick film heater plate in the stack, with one of each pair of supports aligning with the pair of electrodes on the respective thick film heater plate. The supports not only support the stack, but separate each adjacent pair of thick film heater plates to form the slots therebetween. The supports which align with the electrodes of the heater plates electrically interconnect the plates. Each of the electrically connecting supports includes a pair of electrodes for extending therethrough which align with and contact the electrodes in thick film heater plates on opposite sides thereof. An electrical power supply can than be connected at any location along the interconnected circuit of supports and heater plates, to supply power to the entire stack. Although the heater plates could be individually connected to separately controlled power supplies, such an arrangement is more expensive and cumbersome given the greater number of electrical line and power supplies that would be required, and as such is not considered as practical commercially.
The supports comprise a nonconducting material to prevent electrical conduction from the power source to any wafer in a slot. A nonconductive sleeve may surround a portion of each of the electrodes passing through the supports to further insulate the power from the wafers.
A controller may be provided to automatically and remotely control the chamber door led to open and close. The controller may also be connected with the driver or motor and the electric power supply to control their functions.
At least one thermocouple may be provided within the chamber and electrically connected to the controller to provide feedback regarding a temperature inside of the chamber. A more preferred arrangement is to provide three thermocouples 78, 80, 82, one probing the top heater plate, one probing the bottom heater plate, and one probing the middle heater plate or one of a pair of heater plates nearest the middle of the stack if an even number of heater plates is employed. The middle thermocouple is used to provide feedback for temperature control purposes. The top and bottom thermocouples are used for comparison with the reading generated by the middle thermocouple. If a difference between the reading from the middle thermocouple and either one or both of the top and bottom thermocouples becomes more than a predetermined amount, this is an indicator of an operational problem, at which time the operation would be shut down.
Further, a sensor may be mounted on the chamber to detect when a wafer has been placed out of position in the chamber, and the sensor may be electrically connected to the controller to input a message to the controller when a misaligned wafer has been detected.
A heater subassembly for a wafer heating chamber is provided which includes a stack of thick film heater plates electrically interconnected with one another and defining slots therebetween. The slots are dimensioned for receiving wafers. At least a pair of supports are positioned between each pair of interfacing surfaces of the plates.
A support base may be provided to underlie the bottom thick film heater plate of the stack, to further support the stack. A drive shaft extending from the bottom of the stack or support base and is adapted to be driven to traverse the stack.
The supports comprise nonconductive blocks, at least a portion of which have a thickness that defines a height of the slots. Another portion of each nonconductive block is thinner than the thickness defining the height of the slots and forms a portion of a pedestal adapted to support a wafer.
The supports may include spring loaded connectors in combination with a rigid shaft passing therethrough.
These and other objects, advantages, and features of the invention will become apparent to those persons skilled in the art upon reading the details of the heat chamber assemblies and subassemblies as more fully described below.